It’s easy to access Illustrator’s graphic library.
There are many textured, graphic swatches available which you can eventually master and apply to your illustrations as details that create depth.
But, first you must learn where these little gems are stored!
Open a new artboard and go to Window > Swatches to open up the panel.
Of course, the Swatches panel will open up somewhere on your screen.
Focus your attention to the bottom bit of the panel.
Particularly, the lower left corner. If you hover over it, it will read “Swatch Libraries menu.”
Click it and a long list of possibilities will appear. So much to explore!
To find the graphic textures, locate Patterns.
Then, locate Basic Graphics > Basic Graphic_Textures. Click it.
The following panel should pop-up:
To test these out, draw a square (or any other shape that you may like).
Then, select one of the swatches which will automatically fill in the shape.
Keep repeating this process for the other swatches, so that you can familiarize yourself with the possibilities here!